Electrochemical apparatus such as fuel cells, ozone generators, hydroelectrolysis cells, hydrogen generators, deoxygenation apparatus, and the like are known in the art. Also known, and often used in such electrochemical apparatus, are solid polymer ion exchange membranes, including many in which a fluorine-containing polymer is the solid polymer electrolyte.
In an electrochemical apparatus containing an ion exchange membrane, the ion exchange membrane is typically sealed by sandwiching it directly between gaskets. Positioned on both sides of the membrane are electrodes and, outside the electrodes, collectors and feeders for introduction or removal of fluids in the apparatus.
In an electrochemical apparatus in which is contained a fluorine-containing solid polymer ion exchange membrane, some of the above functions may be combined in a composite ion exchange layer. Such a composite ion exchange layer consists at least of a fluorine-containing solid polymer membrane, and may further consist of electrode and/or catalyst materials coated, deposited, or laminated on the solid polymer membrane. Known methods for producing such composite ion exchange layers include:
(1) Formation of an electrode material on the surface of a fluorine-containing solid polymer electrolyte membrane by vapor deposition, sputtering techniques, or the like.
(2) A method in which an electrode material or precursor is precipitated from an aqueous solution onto the surface of the fluorine-containing solid polymer electrolyte membrane, reduced if necessary, and chemically plated.
(3) A method in which an electrode is formed by hot pressing a catalytic substance, using polytetrafluoroethylene (PTFE) or a solid polymer electrolyte as a binder, onto the surface of a fluorine-containing solid polymer electrolyte membrane.
(4) A method in which a fluorine-containing solid polymer electrolyte membrane is coated with an ink or paste solution, and dried to remove the solvent. The ink or paste can be a mixture of an aqueous dispersion of polytetrafluoroethylene and a catalytic material, or a solution containing a fluorine-containing solid polymer electrolyte and a catalytic material or its precursor.
(5) A method in which a catalyst layer is formed on a collector, and this product is laminated to a fluorine-containing solid polymer electrolyte membrane.
(6) A method in which a sheet-form electrode is first formed from a mixture of polytetrafluoroethylene and a catalytic material. The sheet-form electrode is then laminated to a fluorine-containing solid polymer electrolyte membrane. The electrode can be first coated with a solid polymer electrolyte and laminated to the solid polymer electrolyte membrane using the coating as an adhesive.
Fluorine-containing solid polymer electrolyte membranes are generally strongly acidic, containing sulfonic acid groups, etc., and pose problems with corrosion when in contact with many metals. Additionally, many are quite weak, can be relatively easily torn or cracked, and susceptible to mechanical damage caused by sandwiching and compressing between gaskets, or damaged by local heat generation in an electrochemical apparatus.
In Japanese Laid-Open Patent Application No. 5-174845 is disclosed an ion exchange membrane, a peripheral portion of which is reinforced with a solid polymeric film on both sides and sealed in the reinforced portion by gaskets. However, a problem with this construction is that a secure bond between the ion exchange membrane and the reinforcing film is not always obtained, and failure can occur.
As can be seen from the description above, a number of steps can be required in manufacturing and assembling a composite ion exchange layer containing fluorine-containing solid polymer electrolyte membranes in an electrochemical apparatus. To prepare composite ion exchange layers in which electrode and/or catalytic materials are deposited on and supported by the solid polymer electrolyte membrane generally requires that the membrane be masked so that deposition or plating of material does not occur in the gasket or seal areas, and thus increases the number of manufacturing and assembly steps and, accordingly, the amount of manipulation and handling to which the solid polymer electrolyte membrane is subjected.
It is desirable that a fluorine-containing solid polymer electrolyte membrane be provided with means, early in the manufacturing and assembly process, which reinforces and supports the membrane to minimize damage in handling, can serve as a masking means in certain subsequent manufacturing steps, and further provides a seal for the membrane in an electrochemical apparatus.